He still gets upset even though he has a girlfriend now because there’s a good chance that she was his second choice.
He most likely wanted to date you first and foremost and being that you turned him down, he had to make do with a secondary replacement.
He took that personally.
Whenever he sees you or hears about you, it just reminds him of the fact that he’s dating someone that was his second choice and that you turned him down.
That upsets him.
He doesn’t want to be reminded of that.
Yes, this most likely means that he hasn’t truly moved on.
There are still unresolved feelings for you that he tries to forget about but whenever he hears about you or sees you, those feelings come right back up.
He then realizes that he still hasn’t gotten over you and that you still have this kind of effect on him and that annoys him even more.